Binding Between Cyclohexanohemicucurbit[n]urils and Polar Organic Guests

Abstract

Inherently chiral, barrel-shaped, macrocyclic hosts such as cyclohexanohemicucurbit[n]urils (cycHC[n]) bind zinc porphyrins and trifluoroacetic acid externally in halogenated solvents. In the current study, we tested a set of eighteen organic guests with various functional groups and polarity, namely, thiophenols, phenols, and carboxylic and sulfonic acids, to identify a preference toward hydrogen bond–donating molecules for homologous cycHC[6] and cycHC[8]. Guests were characterized by Hirshfeld partial charges on acidic hydrogens and their binding by 1H and 19F NMR titrations. Evaluation of association constants revealed the complexity of the system and indirectly proved an external binding with stoichiometry over 2:1 for both homologs. It was found that overall binding strength is influenced by the stoichiometry of the formed complexes, the partial atomic charge on the hydrogen atom of the hydrogen bond donor, and the bulkiness of the guest. Additionally, a study on the formation of complexes with halogen anions (Cl− and Br−) in methanol and chloroform, analyzed by 1H NMR, did not confirm complexation. The current study widens the scope of potential applications for host molecules by demonstrating the formation of hydrogen-bonded complexes with multisite hydrogen bond acceptors such as cycHC[6] and cycHC[8].

Self-Assembly of Chiral Cyclohexanohemicucurbit[n]urils with Bis(Zn Porphyrin): Size, Shape, and Time-Dependent Binding

“…A family of cycHC[n]s consists of chiral and nonchiral (n = 6, 8, 12) members [37][38][39][40] and features, analogous to all single bridged cucurbiturils [41,42], binding anions inside the macrocycle cavity. Additionally, cycHC[n]s bind hydrogen bond donors and electron-rich organic molecules [43,44]. Upon complexation of chiral cycHC[n]s with achiral and CD silent zinc octaethylporphyrin (ZnOEP) and zinc tetraphenylporphyrin (ZnTPP) in CH 2 Cl 2 , an ICD signal is observed in the region of the porphyrin Soret band [36].…”

Cyclohexanohemicucurbit[8]uril Inclusion Complexes With Heterocycles and Selective Extraction of Sulfur Compounds From Water

“…The latter grants these macrocycles the ability to encapsulate anions ( Buschmann et al, 2005 ; Cucolea et al, 2016 ; Kaabel et al, 2017 ; Assaf and Nau, 2018 ; Reany et al, 2018 ; Vázquez and Sindelar, 2018 ; Andersen et al, 2019 ; Kandrnálová et al, 2019 ; Valkenier et al, 2019 ; Maršálek and Šindelář, 2020 ); in addition, the formation of complexes with acids and some neutral species has been reported in the previous work. In particular, unsubstituted hemicucurbit[ n ]urils ( n = 6, 12) bind phenol derivatives ( Jin et al, 2016a ; 2016b ) and ferrocene ( Jin et al, 2017 ), and cyclohexanohemicucurbit[ n ]urils cycHC [ n ] ( n = 6, 8, 12) ( Li et al, 2009 ; Aav et al, 2013 ; Prigorchenko et al, 2015 , 2019 ; Mishra et al, 2020 ) form external complexes with both inorganic and organic acids ( Öeren et al, 2014 ; Ustrnul et al, 2019 , 2021 ). We envisioned that heterocycles 1–13 have relatively high electron densities compared to carbocycles and may therefore be able to occupy space within the eight-membered cycHC[8] ( Figure 1 ).…”